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Unit 3-Symmetric Key Crypto_Part25

# Unit 3-Symmetric Key Crypto_Part25 - Why not C = E(E(P,K...

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Unit 3 - 49 Today, 56 bit DES key is too small But DES is everywhere: What to do? Triple DES or 3DES (112 bit key) C = E(D(E(P,K 1 ),K 2 ),K 1 ) P = D(E(D(C,K 1 ),K 2 ),K 1 ) Why use Encrypt-Decrypt-Encrypt (EDE) with 2 keys? Backward compatible: E(D(E(P,K),K),K) = E(P,K) And 112 bits is enough Triple DES

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Unit 3 - 50 Why not simplify the process and use Double-DES? I.e., Why not C = E(E(P,K),K) ? Still just 56 bit key
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Unformatted text preview: Why not C = E(E(P,K 1 ),K 2 ) ? A (semi-practical) known plaintext attack Precompute table of E(P,K 1 ) for every possible key K 1 (resulting table has 2 56 entries) Then for each possible K 2 compute D(C,K 2 ) until a match in table is found When match is found, have E(P,K 1 ) = D(C,K 2 ) Result is keys: C = E(E(P,K 1 ),K 2 ) 3DES...
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Unit 3-Symmetric Key Crypto_Part25 - Why not C = E(E(P,K...

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